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| 型号： | LT3972IMSE#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 14/24页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 3.5A 10MSOP |
| 标准包装： | 50 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 0.79 V ~ 30 V |
| 输入电压： | 3.6 V ~ 33 V |
| PWM 型： | 电流模式，Burst Mode? |
| 频率 - 开关： | 230kHz ~ 2.45MHz |
| 电流 - 输出： | 3.5A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 |
| 包装： | 管件 |
| 供应商设备封装： | 10-MSOP 裸露焊盘 |
LT3972
APPLICATIONS INFORMATION
Low Ripple Burst Mode Operation
and Pulse-Skipping Mode
The LT3972 is capable of operating in either low ripple
Burst Mode operation or pulse-skipping mode which are
selected using the SYNC pin. See the Synchronization
section for details.
To enhance ef?ciency at light loads, the LT3972 can be
operated in low ripple Burst Mode operation which keeps
the output capacitor charged to the proper voltage while
minimizing the input quiescent current. During Burst
Mode operation, the LT3972 delivers single cycle bursts of
current to the output capacitor followed by sleep periods
where the output power is delivered to the load by the
output capacitor. Because the LT3972 delivers power to
the output with single, low current pulses, the output ripple
is kept below 15mV for a typical application. In addition,
V IN and BD quiescent currents are reduced to typically
30μA and 90μA respectively during the sleep time. As
the load current decreases towards a no-load condition,
the percentage of time that the LT3972 operates in sleep
mode increases and the average input current is greatly
reduced resulting in high ef?ciency even at very low loads.
See Figure 4. At higher output loads (above 140mA for
the front page application) the LT3972 will be running at
the frequency programmed by the R T resistor, and will be
operating in standard PWM mode. The transition between
PWM and low ripple Burst Mode operation is seamless,
and will not disturb the output voltage.
If low quiescent current is not required the LT3972 can
operate in pulse-skipping mode. The bene?t of this mode
V SW
5V/DIV
I L
0.2A/DIV
V OUT
10mV/DIV
is that the LT3972 will enter full frequency standard PWM
operation at a lower output load current than when in
Burst Mode operation. The front page application circuit
will switch at full frequency at output loads higher than
about 60mA. Select pulse-skipping mode by applying
a clock signal or a DC voltage higher than 0.9V to the
SYNC pin.
BOOST and BIAS Pin Considerations
Capacitor C3 and the internal boost Schottky diode (see
the Block Diagram) are used to generate a boost volt-
age that is higher than the input voltage. In most cases
a 0.22μF capacitor will work well. Figure 2 shows three
ways to arrange the boost circuit. The BOOST pin must be
more than 2.3V above the SW pin for best ef?ciency. For
outputs of 3V and above, the standard circuit (Figure 5a)
is best. For outputs between 2.8V and 3V, use a 1μF boost
capacitor. A 2.5V output presents a special case because it
is marginally adequate to support the boosted drive stage
while using the internal boost diode. For reliable BOOST pin
operation with 2.5V outputs use a good external Schottky
diode (such as the ON Semi MBR0540), and a 1μF boost
capacitor (see Figure 5b). For lower output voltages the
boost diode can be tied to the input (Figure 5c), or to
another supply greater than 2.8V. Tying BD to V IN reduces
the maximum input voltage to 28V. The circuit in Figure 5a
is more ef?cient because the BOOST pin current and BD
pin quiescent current comes from a lower voltage source.
You must also be sure that the maximum voltage ratings
of the BOOST and BD pins are not exceeded.
The minimum operating voltage of an LT3972 application
is limited by the minimum input voltage (3.6V) and by the
maximum duty cycle as outlined in a previous section. For
proper start-up, the minimum input voltage is also limited
by the boost circuit. If the input voltage is ramped slowly,
or the LT3972 is turned on with its RUN/SS pin when the
output is already in regulation, then the boost capacitor
may not be fully charged. Because the boost capacitor is
charged with the energy stored in the inductor, the circuit
will rely on some minimum load current to get the boost
circuit running properly. This minimum load will depend
V IN = 12V
V OUT = 3.3V
I LOAD = 10mA
5μs/DIV
3972 F04
on input and output voltages, and on the arrangement of
the boost circuit. The minimum load generally goes to
Figure 4. Burst Mode Operation
zero once the circuit has started. Figure 6 shows a plot
3972fa
14
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| LT3972IMSE-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:33V, 3.5A, 2.4MHz Step-Down Switching Regulator with 75μA Quiescent Current |
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| LT3973EDD#PBF | 功能描述:IC REG BUCK ADJ 0.75A 10DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V，1.5V，1.8V，2.5V 输入电压:2.7 V ~ 20 V PWM 型:- 频率 - 开关:- 电流 - 输出:50mA 同步整流器:是 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 包装:带卷 (TR) 供应商设备封装:10-MSOP 裸露焊盘 |
| LT3973EDD#TRPBF | 功能描述:IC REG BUCK ADJ 0.75A 10DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V，1.5V，1.8V，2.5V 输入电压:2.7 V ~ 20 V PWM 型:- 频率 - 开关:- 电流 - 输出:50mA 同步整流器:是 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 包装:带卷 (TR) 供应商设备封装:10-MSOP 裸露焊盘 |
| LT3973EDD-3.3#PBF | 功能描述:IC REG BUCK 3.3V 0.75A 10DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:250 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V 输入电压:2.05 V ~ 6 V PWM 型:电压模式 频率 - 开关:2MHz 电流 - 输出:500mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:6-UFDFN 包装:带卷 (TR) 供应商设备封装:6-SON（1.45x1） 产品目录页面:1032 (CN2011-ZH PDF) 其它名称:296-25628-2 |
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